This invention relates to semiconductor lasers and, more particularly, to heterostructure semiconductor lasers that are doped with deep-level traps.
Ordinary heterostructure semiconductor lasers generally exhibit an efficiency in terms of elecrical input versus optical output of about 20 percent. Heterostructure semiconductor lasers of the type under consideration herein are well known to those skilled in the art. See, for example, U.S. Pat. No. 3,758,875 issued on Sept. 11, 1973 to I. Hayashi and U.S. Pat. No. 3,893,044 issued on July 1, 1975 to W. P. Dumke. Ordinary photodetectors without avalanche gain exhibit an efficiency of about 80 percent. It is therefore impossible to combine an ordinary photodiode with a semiconductor laser and achieve a combination that exhibits optical gain. In an effort to achieve optical gain, some have proposed that an avalanche detector be combined with a laser thereby creating optical circuits that may be connected in tandem. Avalanche photodiodes, however, require a high electrical bias voltage and it is therefore difficult to combine this type of photodetector into logic circuits exhibiting AND and OR functions. it would be highly advantageous to create a semiconductor laser whose efficiency is greater than one, thereby permitting the creation of optical logic arrays.
Some studies have been conducted to determine the effect of deep-level traps in the active region of a double heterostructure semiconductor laser. See, for example, the article entitled "Microscale Degradation in (GaAl) Double-Heterostructure Diode Lasers" by D. Kato, Applied Physics Letters, Vol. 31, No. 9, November 1977, pp. 588-590. As pointed out in the Kato article, these deep-level traps can result in self-sustained pulsations. As also pointed out in the Kato article, the deep-level traps can be formed or developed by crystal imperfections and/or the presence of added impurities.